Most modern electronic equipment requires a power supply to provide a direct current (DC) operating potential to the electronic components contained therein. Common types of electronic equipment which use power supplies include personal computers, energy systems, telecommunication systems, audio-video equipment, consumer electronics, automotive components, and other devices which utilize integrated circuits, semiconductor chips, or otherwise require DC operating potential. Most, if not all, semiconductor components require a low voltage DC operating potential. However, many sources of electric power are alternating current (AC), or high voltage DC, which must be converted to low voltage DC for the electronic equipment.
In one common arrangement, the AC/DC power supply receives an AC input voltage, e.g., between 110 and 240 VAC, and converts the AC input voltage to the DC operating voltage. The AC voltage is routed through a full-wave rectifier bridge and filtered to produce a high voltage DC signal. The high voltage DC signal is processed through a pulse width modulated (PWM) controller and transformer assembly to generate the low voltage, regulated DC output voltage, which is used as the operating potential for the semiconductor components and other devices requiring low voltage DC supply in the electronic equipment. The low voltage DC signal is typically in the range of 1 to 12 VDC. In other cases, a DC/DC power supply receives a high voltage DC signal and provides the low voltage DC signal necessary for the electronic equipment.
Power supplies are generally high production units, designed to operate at a specific voltage level, which may be adjustable within a narrow range. The power supply maximum output current capability is set by the design components. Manufacturers sell power supplies over a range of discrete output voltages and output current capability, sometimes specified by a power rating. To select a power supply, the original equipment manufacturer (OEM) will select the desired power supply from the vendor's catalog. If the available power supplies do not have the proper power rating for the electronic equipment, then OEMs are known to connect two or more power supply modules in parallel to increase the available output current. The process of connecting power supply modules in parallel can be accomplished using a popular approach known as the droop method. Theoretically, connecting two identical power supply modules in parallel maintains the same output voltage while doubling the output current.
The droop method allows OEMs to increase current capability and use the same standard power supply module for many different maximum load requirements. However, the droop method may lead to poor load regulation among the parallel-connected power supply modules due to the variation in the output voltage and load current of each power supply.
A need exists to connect multiple power supply modules in parallel while maintaining good load regulation.